Reversible structural rearrangements ("breathing") of metal-organic frameworks (MOFs) are interesting and complex phenomena with many potential applications. They are often triggered by small amounts of adsorbed guest molecules; therefore, the guest-host interactions in breathing MOFs are intensively investigated. Due to the sensitivity limitations, most analytical methods require relatively high concentrations of guests in these studies. However, because guest molecules are not "innocent", breathing behavior may become suppressed and unperturbed structural states inaccessible. We propose here the use of guest nitroxide molecules in tiny concentrations (such as 1 molecule per 1000 unit cells), which serve as spin probes for electron paramagnetic resonance (EPR), for effective study of breathing phenomena in MOFs. Using a perspective MIL-53(Al) framework as an example, we demonstrate the great advantage of this general approach, which avoids perturbation of the framework structure and allows in-depth investigation of guest-host interactions in the breathing mode.
Thermally stable organic diradicals with at riplet ground state along with large singlet-triplet energy gap have significant potential for advanced technological applications.A series of phenylene-bridged diradicals with oxoverdazyla nd nitronyl nitroxide units were synthesized via ap alladiumcatalyzedc ross-coupling reaction of iodoverdazyls with an itronyl nitroxide-2-ide gold(I) complex with high yields.T he diradicals exhibit high stability and do not decompose in an inert atmosphere up to 180 8 8C. Fort he diradicals,b oth substantial AF (DE ST %À64 cm À1)a nd FM (DE ST ! 25 and 100 cm À1)intramolecular exchange interactions were observed. The sign of the exchange interaction is determined both by the bridging moiety (para-or meta-phenylene) and by the type of oxoverdazylb lock(C-linked or N-linked). Upon crystallization, diradicals with the triplet ground state form unique onedimensional exchange-coupled chains with strong intra-and weak inter-diradical ferromagnetic coupling.
Thermally resistant air-stable organic triradicals with a quartet ground state and a large energy gap between spin states are still unique compounds. Moreover, stable triradicals with bridging units of the ethylene-1,1-diyl type and ferromagnetic coupling are limited to the family of nitroxides. In this work, for the first time, we designed and prepared the triradical having a quartet ground state based on oxoverdazyl and nitronyl nitroxide radical fragments. The triradical and appropriate triplet diradical precursor were synthesized via a palladium-catalyzed cross-coupling reaction of diiodoverdazyl with nitronyl nitroxide-2-ide gold(I) complex. Both the di-and triradical are air-stable and possess good thermal stability with decomposition onset at ∼160 °C in an inert atmosphere. X-ray diffraction analysis of single crystals confirmed the presence of verdazyl and nitroxide radical centers. In the diradical, the verdazyl and nitronyl nitroxide centers showed fully reversible redox waves. In case of the triradical, the electrochemical processes occur practically at the same redox potentials but become quasi-reversible for the nitroxide moieties. Magnetic properties of the di-and triradical were characterized by a SQUID magnetometry of polycrystalline powders and by EPR spectroscopy in different matrices. Collected data analyzed using of the highlevel quantum chemical calculations confirmed that the di-and triradical have high-spin ground states. Unique high stability of prepared verdazyl-nitronylnitroxyl triradical opens new perspectives for further functionalization and design of high-spin systems with four or more spins.
Solution-grown single crystals of furan/phenylene co-oligomer combine efficient charge transport properties and high fluorescence efficiency.
The system [FeL2](BF4)2 (1)-EtOH-H2O (L is 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-(pyridin-2-yl)-6-methylpyrimidine) shows a complicated balance between the relative stabilities of solvatomorphs and polymorphs of the complex [FeL2](BF4)2. New solvatomorphs, 1(LS)·EtOH·H2O and β-1(LS)·xH2O, were isolated in this system. They were converted into four daughter phases, 1(A/LS), 1(D/LS), 1(E/LS)·yEtOH·zH2O and 1(F/LS). On thermal cycling in sealed ampoules, the phases 1(LS)·EtOH·H2O and β-1(LS)·xH2O transform into the anhydrous phase 1(A/LS). The hysteresis loop width for the (A/LS) ↔ (A/HS) spin transition depends on the water and ethanol contents in the ampoule and varies from ca. 30 K up to 145 K. The reproducible hysteresis loop of 145 K is the widest ever reported one for a spin crossover complex. The phase 1(A/LS) combines the outstanding spin crossover properties with thermal robustness allowing for multiple cycling in sealed ampoules without degradation. The kinetics of the 1(A/LS) → 1(A/HS) transition is sigmoidal which is indicative of strong cooperative interactions. The cooperativity of the 1(A/LS) → 1(A/HS) transition is related to the formation of a 2D supramolecular structure of the phase 1(A/LS). The activation energy for the spin transition is very high (hundreds of kJ mol(-1)). The kinetics of the 1(A/HS) → 1(A/LS) transition can either be sigmoidal or exponential depending on the water and ethanol contents in the ampoule. The phases 1(D/LS) and 1(F/LS) show gradual crossover, whereas the phase 1(E/LS)·yEtOH·yH2O shows a reversible hysteretic transition associated with the solvent molecule release and uptake.
Amination of pentafluoropyridine, 2,3,5,6 tetrafluoropyridine, 4 chlorotetrafluoropyridine, 3,5 dichlorotrifluoropyridine, octafluorotoluene, α,α,α,2,3,5,6 heptafluorotoluene, deca fluoro m xylene, decafluorobiphenyl, hexafluorobenzene, and pentafluorobenzene with liquid ammonia was investigated. Bis aminodefluorination temperatures for the majority of sub strates were shown to exceed significantly the corresponding temperatures of monoamino defluorination. The optimal conditions for selective preparation of mono and diamino polyfluoro(het)arenes were elucidated. An efficient method for isolation of particular polyfluorophenylenediamines from product mixtures formed in nonselective reactions of pentafluorobenzene and hexafluorobenzene with aqueous ammonia based on complexation with a crown ether is proposed. N. N. Vorozhtsov´s school made a considerable con tribution to the chemistry of polyfluoroaromatic com pounds: methods for the synthesis 1 and functionali zation 2,3a of base polyfluoroarenes were developed. Cur rently many polyfluoroarene derivatives are demanded for high tech processes and materials. In particular, diamino and dihydroxy(poly)fluoroarenes serve as struc tural blocks in the synthesis of polyimides used in fiber optic and thin film light guides, nanofilters, and mem branes, dielectric coatings, liquid crystalline displays, op tical diodes, laser media, etc. 4 Polyfluorinated amines of the benzene and pyridine series are used in the synthesis of biologically active compounds. 5It is known 6 that aminodehalogenation of arenes in aqueous ammonia, which is usually carried out in steel autoclaves at high temperatures (up to 250 °C), is often accompanied by competing transformations of arenes such as hydroxy and/or hydrodehalogenation involving water and the autoclave material. The version of the method of polyfluoroarene amination developed in this study im plies the use of liquid ammonia as both the reagent and the reaction medium. The possibility of aminodefluorina tion of some polyfluoroarenes with enhanced electrophi licity in liquid ammonia has been demonstrated previ ously. 7 The efficiency of liquid ammonia as a medium for aromatic nucleophilic substitution has been described in a review. 8 Note that the temperatures suitable for the work with liquid ammonia are limited by the range from -70 to 120 °C (m.p. -78 °C, critical point 133 °C). 9 It follows from analysis of published data that arene amino dehalogenation in liquid ammonia has a higher rate than that in aqueous ammonia; therefore, the processes are carried out at relatively low temperatures and the side reactions are minimized.The purpose of this study was to elucidate the condi tions for mono and diamination of polyfluorinated ben zene and pyridine derivatives in liquid ammonia, which are optimal as regards the selectivity and product yield, to develop simple and practically feasible techniques for separation of mixtures of amino compounds, and to syn thesize new high purity polyfluoroaromatic diamines de manded in high tech applic...
The cocrystallization of 1,2,5-chalcogenadiazoles (chalcogen E = S, Se, and Te) with cyclic polyethers 18-crown-6 (18-c-6) and dibenzo-18-crown-6 (db-18c-6) yielded the molecular complexes characterized by X-ray diffraction and thermogravimetry/differential scanning calorimetry techniques together with density functional theory (DFT) calculations and quantum theory of atoms in molecule and natural bond orbitals analysis. The complexes are bound by multiple secondary bonding interactions, the most important of which reflects the Lewis ambiphilicity of 1,2,5-chalcogenadiazoles and includes charge transfer from O atoms of the ethers onto E atoms of the chalcogenadiazoles (i.e., chalcogen bonding), and the back-donation from E to O. For complexes of 18-c-6, the DFT-calculated energies of bonding interactions correlate with the melting temperatures of the complexes, as well as with the atomic number of E and the size of the E-associated σ-holes but not with the maximum of molecular electrostatic potential at the σ-holes. Taking into account the previous results, the Lewis ambiphilicity of 1,2,5-chalcogenadiazoles may be used for applications in crystal engineering.
Long-range exciton diffusion facilitates efficient exciton harvesting in a lightly-doped organic semiconductor crystal.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.